Conventional rod pumps are placed near the bottom of a casing in an oil well above a perforated section of the casing. The pump draws oil into the perforated section of the casing, through the pump, and into a tubing. The pump also lifts the oil up to the surface through the tubing by way of a lock, such as an API lock.
The simplest rod pump consists of a plunger which reciprocates inside a longer pump cylinder. The pump cylinder is secured to the tubing.
The plunger is sized to create a fluid seal between the outer diameter (“OD”) of the plunger and the inner diameter (“ID”) of the pump cylinder. The rod pump has two one-way check valves: a standing valve at the bottom of the pump and a traveling valve in the plunger.
A sucker rod string is connected to a pull rod on one end and is also connected at the other end to a surface pumping unit (often called a grasshopper). In turn, the opposite end of the pull rod is passed through a rod guide to the plunger of the pump. The grasshopper moves the sucker rod string (and the connected pull rod and plunger) up and down creating the up and downstroke of the plunger. As the sucker rod string and pull rod are lifted by the surface pumping unit, the plunger moves upward within the pump cylinder.
As the plunger moves upward, it lifts the oil within the tubing upward toward the surface and forms a pump chamber within the pump cylinder between the pump bottom and the plunger. As the plunger moves upward, pressure decreases in the pump chamber allowing formation pressure to exceed pressure in the pump chamber, which in turn, causes the standing valve to open and oil to enter into the pump chamber through the open standing valve.
In an ideal environment, as the plunger moves downward during the downstroke, the pump chamber decreases in volume and causes the pressure in the pump chamber to exceed the head pressure from fluid in the tubing above the pump and allows the traveling valve to open and oil to pass into the pump chamber above the traveling valve. However, no oil enters the pump chamber below the traveling valve during the downstroke as the head pressure ensures that the standing valve remains closed. During the upstroke, as the plunger moves upward, the pump chamber below the traveling valve increases in volume and causes pressure in the pump chamber below the traveling valve to decrease. Once the pump chamber pressure is lower than the head pressure, the head pressure forces the traveling valve closed. With the traveling valve closed, the standing valve will open once the chamber pressure is less than the formation pressure. Thus, even in an ideal environment, through approximately one-half the pump cycle, the standing valve is closed and no oil enters the pump chamber.
Further, often there are problems that can occur downhole that further decrease the operational efficiency of conventional rod pumps. One such problem is gas locking. In a typical oil well, oil with dissolved gas or gas from the surrounding formations enter the conventional rod pump. If the ratio of gas to oil entering the pump becomes too high, gas locking can occur. More specifically, the presence of too much gas in the pump chamber results in a peak pressure within the pump chamber that is insufficient to overcome the hydrostatic pressure, resulting in the traveling valve remaining closed on the downstroke. Similarly, the presence of too much gas also precludes sufficient reduction in chamber pressure during the upstroke to open the standing valve. Under such a gas locked condition, the pump simply reciprocates without moving any oil, wasting substantial energy and prematurely wearing the component parts of the pump.
Further, due to the high cost of energy, oil pumps are often shut down in frequent intervals in order to save energy costs. During periods when the pump is shut down, sand and silt mixed in the oil collected in the tubing above the pump begins to settle onto and ultimately reenters the pump. The sand and silt that accumulates in the pump during pump shut down periods causes premature wear on the plunger and traveling valve.
Thus, there is a need for a device that easily mounts to a conventional rod pump that increases its efficiency by increasing the time the standing valve remains open during the pump's operation. There is a further need for a device that reduces the risk of gas locking. There is a further need for a device that prohibits sand and silt mixed with oil in the tubing above the pump from settling back into the pump during periods when the pump is shut down.